(a) Field of the Invention
The present invention relates to a gear train for an automatic transmission used in vehicles. More particularly, the invention relates to a gear train for a 5-forward speed and 1-reverse speed automatic transmission.
(b) Description of the Related Art
Generally, automatic transmission systems for vehicles are provided with a transmission control unit (TCU) which automatically controls shift ratios according to changes in a running condition of the vehicle.
The typical TCU controls a plurality of friction elements provided in a gear train to either operative or inoperative states to select one of the three essential elements of a planetary gear set (i.e., a sun gear, a ring gear, or a planetary carrier) to be an input element, a reaction element, or an output element, thereby controlling an output number of revolutions.
Particularly, a gear train that can realize 5-forward speeds and 1-reverse speed comprises a plurality of heavy and large-sized clutches and brakes and a plurality of inoperative friction elements, resulting in deterioration of power and space efficiencies.